The ash produced in big boilers is so high in quantity, that to utilize it completely converting into useful product is not always possible. In such conditions ash is required to be dumped in ash pond / ash pits which are usually far away from the plant area. The most efficient method of disposing ash in such cases is by pumping it in form of slurry through cast basalt pipes.
Slurry pumping can be classified in Low / Medium density and High Density depending on the slurry concentration. The carrying medium is always water.
In case of Coal fired boilers DEMECH system requires less water thereby saving water and also needs lesser headroom below the furnace.
Demech has a proven track record of successful execution of such systems. The scope typically comprises of design, supply, erection & commissioning of long distance Ash slurry disposal system.
- Flow quantity of Slurry and pressure required are the basic parameters required for designing the system. However, these two parameters in turn depend on many other conditions like rate of ash to be disposed, pipeline distance, pipeline profile, density of slurry, viscosity of slurry etc. Moreover ash is highly abrasive and pipeline wear also needs to be considered. A critical aspect of system is selection of slurry velocity in the pipeline which should be low to minimize abrasion but high enough to avoid settling of Ash in the pipeline.
- Slurry with low or medium concentration (usually 45% to 50% by weight) can be pumped using centrifugal slurry pumps. The viscosity of slurry does not have much effect for such conditions while calculating pressure requirement, but as the slurry concentration increases the viscosity effect has a dominant effect for calculating pressure requirement. Generally ash slurry pumping beyond 65% in not feasible, as high concentration slurry requires extremely high pressure which increases exponentially as per the concentration. Such high pressures can be developed using piston diaphragm pumps. These pumps can develop very high pressures but are very costly and have a very high maintenance cost. The high pressures result in higher power consumption though the water requirement is lower in this system.
- The advantage of water saving in high concentration pumping gets nullified when it is compared with the low / medium concentration slurry pumping, accompanied with water recovery system. In spite of double pumping in low concentration slurry pumping, the power requirement is either low or equal. Another advantage of this systems is the easy maintenance and less cost of spares, that makes the system more viable.